Input conveyor systems are known in the prior art which will receive a train of paper sheets of different sizes and pass them to an associated folder (such as an accordion-type folder) which automatically folds them into packets according to a desired folding routine for each size of sheet. U.S. Pat. No. 3,961,781 of Roger S. Funk, issued Jun. 8, 1976, describes such a system, in which the sizes of successive sheets fed into the folder system are automatically sensed on the input conveyor, as by photodetectors, to produce signals representative of the size of each sheet as it enters the folder; these signals are then used to control the subsequent folding action in a manner appropriate to the size of the sheet being folded.
The space between successive sheets leaving the printer in the print/fold process is called the "intercopy gap". Universal-type folders which must adapt to a variety of different printers cannot be used if there is an insufficient intercopy gap. This is often the case because of the inherent difference in mechanics between the printer which is continuous, and the folding machine which must complete its operation on a first sheet before the next sheet is received.
For relatively short sheets, a short intercopy gap may be compensated for by merely increasing the speed of the folder relative to the printer. However, this compensation is not possible with a longer sheet which, while its leading edge is entering the folder, still has its trailing portion constrained by the conveyor system in the printer. When both the printer and folder are operating simultaneously on opposite ends of a relatively longer sheet, the speeds of the printer and the folder must be equal to prevent the buckling or tearing of the sheet. Equalizing the speeds of the printer and folder, however, negates the possibility of simply increasing the folder speed relative to the printer and thus the intercopy gap problem persists.
One solution to this problem is to create a very long paper path in the conveyor between the printer and folder that is greater than the longest printed sheet. Then, since the two machines will never be operating on the same sheet at the same time, the requirement mentioned above for equalizing the speeds is eliminated. By using a very long paper path, a printer intercopy gap which is too short may be compensated for by simply increasing the speed of the folder relative to the printer. Since the print ahead is always moving at a faster speed, the intercopy gap increases to the desired distance as the sheets travel across the conveyor to the folder.
The above solution, however, poses a severe disadvantage; namely, greatly increased floor space required for a very long, flatbed conveyor between printer and folder to provide the long paper path. Floor space occupied by the conveyor may be saved by employing a serpentine paper path, or utilizing a conveyor system which allows the sheet to loosely accumulate between the printer and folder; but these alternatives are inadequate, since accurate control of the position and movement of the sheet is lost. Furthermore, the other benefits of a flatbed, horizontal conveyor which may employ sensors for determining sheet speed, width and length are also forfeited.